Doppler antenna array employing multiple slotted waveguides with feed switching



June 2, 1964 M. J. MORAN 3,135,959

IPLE SLOTTE D WAVEGUIDES WITH FEED SWITCHING Original Filed Sept. 30, 1957 3 Sheets-Sheet l DOPPLER ANTENNA ARRAY EMPLOYING MULT June 2, 1964 M. J. MORAN 3,135,959

DOPPLER ANTENNA ARRAY EMPLOYING MULTIPLE SLOTTED WAVEGUIDES WITH FEED SWITCHING Original Filed Sept. 30 1957 3 Sheets-Sheet 5 United States Patent Ofi ice.

3,135,959. Patented June 2, 1964 3,135,959 DOPPLER ANTENNA ARRAY EMPLOYING MUL- TIPLE SLOTTED WAVEGUIDES WITH FEED SWITCHING Michael James Moran, London, England, assignor to Decca Limited, a British company Continuation of application Ser. No. 687,327, Sept. 30, 1957. This application Mar. 24, 1960, Ser. No. 17,436 17 Claims. (Cl. 343-768) This invention relates to aerials for use in microwave Doppler airborne navigational equipment for determining the ground speed and drift of an aircraft.

This application is a continuation of my application Serial No. 687,327 entitled Aerial Systems and filed on September 30, 1957, now abandoned.

Aerials for this purpose have to provide four directional beams all directed onto the ground, one pointing forwardly to the port side, the second forwardly to the starboard side, the third rearwardly to the port side and the fourth rearwardly to the starboard side. The first and fourth beams have to be employed simultaneously as do the second and third. For this particular navigational system it is necessary to employ linear arrays, such as slotted waveguides, the array being mounted substantially horizontally on the aircraft in a fore and aft direction. The array may, if necessary, be partially or wholly stabilised to maintain it horizontal.

Aerials for use with the navigational equipment described above are used both for transmitting and receiving, but for convenience in terminology reference will only be made to the radiation of beams in the following description. It will be understood that aerials would be used both for receiving and for transmitting.

Heretofore two alternative forms of antenna have been employed. In one form, four separate linear array systems in the form of four waveguides are arranged horizontally in the fore and aft direction of the aircraft, the four array systems being arranged to have their beams pointing in the required directions. In the other construction, two linear array systems have been employed, one providing a beam pointing forward and the other pointing aft. Each of the array systems has been provided with a mechanically movable reflector for deflecting the beam to either the port or starboard side, the two reflectors being coupled and arranged so that when the forward beam is deflected to port the aft beam is defiected to starboard and vice versa.

It is one of the objects of the present invention to provide a form of stacked array which will produce the required two pairs of beams without any mechanical switching of reflectors and without any limitation of the squint angle.

According to this invention, an aerial system for use in midfowave Doppler airborne navigational equipment comprises a stacked array formed of two sets of rows of radiating slots, the slots in each row of one set being phased radiating slots and the slots of each row of the other set being anti-phased radiating slots, whereby, if the rows are arranged in the fore-and-aft direction in an aircraft, one set of rows will produce a forwardly directed beam and the other set of rows a rearwardly-directed beam, all the rows in each set being fed from a common transverse feed guide, and the phase relationship of the feeds to the rows in one set being different from that of the feeds to the rows in the other set so as to produce deflections of the two beams in opposite directions transversely to the direction of the rows. The length of the rows and the number of rows in each set is determined by the required angular widths of the beams. Such an arrangement produces two beams. As is described later,

the second pair of beams may be provided using the same array by switching the feed system so that either the transverse feed guide for each set of rows is fed alternately from opposite ends or the various rows are fed alternately from opposite ends. Each row of slots may be formed by a rectangular wave guide, the slots being formed in one face of the Wave guide and, most conveniently, the slots are formed in a narrow face of the wave guide.

The squint angle B for each set, provided the rows of each set are fed in anti-phase, as is necessary for the minimum squint angle, is given by the expression:

where 7\ is the wavelength of the signals A is the guide wavelength in the feed guide and sis the effective spacing of the couplings to the feed guide.

Preferably, the feeds to the various rows are phased to produce equal squint angles. To make the two squint angles equal, the guide wavelengths and the effective spacings for the points along the transverse feed guide feeding the two sets respectively may be chosen, in accordance with the above equation so as to give values of ,8 of equal magnitude but opposite sign. This may be done by a suitable choice of theguide wavelengths or of the spacing or of both. For example the two squint angles for the two rows may be made equal by the use of feed guides having diiferent sections giving different guide wavelengths for the two transverse feed guides, the spacings of the rows for the two sets being made equal. Alternatively, the squint angles for the two rows may be made equal by the use of diiferetn spacings for the two sets of different spacings for the two sets of rows of the feed points along the transverse feed guide-feeding the rows in each set, and in this latter arrangement conveniently the spacing of the rows of each set is made equal to the spacing of the feed points along the transverse feed guides.

A single transverse feed guide may be used for feeding both sets of rows, but generally it will be more convenient to employ two transverse feed guides in parallel for the two sets of rows.

The two sets of rows of radiating slots, as described above, will produce one pair of beams, one directed for ward and to one side and the other directed backwardly and to the other side, assuming the rows extend in the fore-and-aft direction of the aircraft. In order that the beams may be switched to change from one pair to the other as required for airborne Doppler navigational systems, in one arrangement, switch means may be provided for feeding the transverse feed guide for each set of rows from either end so as to effect the necessary phase alteration of the feeds to the various rows required for such beam switching. Said switch means may comprise a single switch for switching feeds to two separate transverse feed guides in parallel separately feeding the two sets of rows if two such parallel feed guides are employed.

Each row may be fed from a coupling slot in the transverse feed guide and, in this case the slot conductances would normally be made symmetrical so that similar radiation patterns are obtained with either end of a transverse feed guide being fed. By similar radiation patterns, it is meant that the beams have the same shape although, by feeding from opposite ends of the feed guide, they would be directed to opposite sides of the aircraft.

In another arrangement for changing the beams from one pair to the other, switch means are provided for feeding each set of rows from one or other of two separate transverse feed guides at opposite ends of the rows of radiating slots whereby the depression angle (that is the radiating slots.

angle of depression from the horizontal in a vertical foreand-aft plane) may be varied to switch a forward beam to a rearward beam or vice versa. Conveniently two transverse feed guides are provided each feeding both sets of rows. in this arrangement, preferably the radiating slots have symmetrical conductances'so that similar radiation patterns are obtained witheither end'of the rows of radiating slots being fed. V V V i a The rows of one set may be arranged alternately with the rows'of the other set, or'the rows of one set may be arranged in a group to one sideof the rows of the other set.

The aerial system would be arranged in an aircraft with the rows of slots in lines extending fore and aft of the aircraft and with all the radiating slots in a substantial ly horizontal plane when the aircraft is in a normal fly- 7 ing' attitude. Stabilising'means may be provided to the guides 29 to 25 have radiating slots of which alter nate slots radiate in anti-phase' as indicated diagrammati- ,cally by the opposite slopes of the alternate slots, If a single one of the'waveguides 20-25 is considered as lying in the fore-and-aft direction'of the aircraft with the A V radiating slots facing downwardly and thi s waveguide, is

fed from one end, it will radiate a beam which will point in'a direction in the fore-and-aft plane dependent on the. slot spacingfand. guide wavelength, the angular 'dire'ctionf i from the vertical being given by the expression:

where 1 a stabilise the aerial system in'thehorizontal plane or to- FIGURE 2 is a diagram illustrating one form of'aer- FIGURE 3 is an isometric View from the underside, partly cut away, of one embodiment of the aerial system of FIGURE 2;

- FIGURE 4 is a diagram illustrating a switching ar I rangement for use in the aerial system Of'FIGURE 3';

FIGURE 5 is a diagram similar to? FIGURE 2, but of a second form of aerial system; ,7

FIGURE 6 is a perspective view from the underside, partly cut away, of one embodiment of the aerial system of FIGURE 5; 7 FIGURE 7 is 'a plan view from the top of part of the aerial system of FIGURE 5; and 1 FIGURES 8 and 9 arediagrams, similar to FIGURES 2 and 5, of yet further forms of aerial system.

FIGURE 1 is an explanatory borne navigational equipment for determining the ground speed and drift of an aircraft. An aircraft is shown diagrammatically at 10 and the :point 0 represents a point on the ground vertically below the aircraft. This point lies on the track of the aircraft which is shown as the line X-X. OY is normal to theline X'-X through the point 0 on the ground plane. The aerial system is required. to provide four directional beams ofwhich the intersections with the ground plane are shown at 11, 12, 13 and 14. For convenience the four beams will be referred to as the beams ll, .12, 13 and 14- respectively and it will be seen that the beam 11 is directed forwardly to the port side, the beam 12 is directed rearwardly to the starboard'side, and the beam 13 forwarly to the starboard side, and the beam 14 rearwardly to the" port side. a

' ial system for an airborne Doppler navigational system,

diagram showing the form of radiation pattern required fora Doppler air 6 is the depression angle of theaxis of the beam from' the horizontal 2 is the wavelength of the signals 1 V l is the guide wavelength in theslotted waveguide. s is the spacing of the slots along the guide, and 11=O, ;2etc. V, a When the spacing of the slots is such that on1yn=0 gives a solution, there is only one main beam and: I I V i s 1 For the "waveguides. 26 31 with'phased radiating slots, 7 thedepression angle 6 isgiven by the expression:

. mart. and if there is to be only one beam,

' J V 7X n will thus be m that if the by feeding these guides in a suitablephaserelationship, the beams are directed to one side or other of theforeand-aft plane through the aircraft. The angular deflection sideways from the vertical plane is referredtosas the; squint angle.v If th forwardly-directed beam is deflected I to the port side, that is to say to form the beam 11, then 7 by reversing the. phase relationship of theifeeds into the Beams 11 and 12 have to be employed simultaneously as do beams 13, 14, but beams 11 and 12 are not required at the same time as beams 13 and'14 and thus a switching system may be employed so that in alternate intervals V of time, beams 11 and 12 are simultaneously radiated,

then beams 13 and 14.

lt will be understood, as previously stated',.that the aerial system would be us ed both for receiving and for transmitting, although for convenience'in terminology,

reference will be made more particularlyto the radiation of beams inthe following description'.'

Referring to FIGURE 2, there are shown two stacked arrays which form a plurality of wave guides having One of the arrays is formed from waveguides 20 to 25 and the other from Waveguides 26 to 31. These waveguides are represented diagrammatical-j ly in FIGURE 2 by lines and the radiating slots are repwhere 7 resented by short lines extending transversely across the V waveguides. Each of the guides 26 to 31 has slots which all radiate in phase, this being indicated by. the similar slopes of the transverse lines representing the slots, whilst the spacing of the feeds to the various rows along'the.

guides producing this'beam', the beam will be deflected to the starboard side and thus produce the beam 13 1 V The squint angles'depend on the relative phases ofithe feeds to the various rows, and thus on transverse feed guide and the guide wavelength alongthat guide. To obtain the minimum squint angle, the various rows must be fed in anti-phase, that is tosay, alternate rows are fed in opposite phase, and the squint angle ,8 is

given the expression: J a x x A is the guide wavelength in the: feed guide, and

is is theeffective spacing along the feed guide of the conplings to the various rows. I v V v It will be seen thatthis squint angle depends on the guide wavelength and the spacing of the couplings to the rows "and, to produce equal squint angles on eitherside of the vertical plane for the twobeams'from the two sets of rows, therows must be fed'in asuitablephase relationship. All the rows of the two sets might 'be fed from the single transverse feed guide and'the spacing of the rows 26 v I slot spacing in the two setsof waveguides is equal toaquarter of a guide wave-. length, the two beams will be at equal and opposite depression angles, 'that'istosay, one beam will be diij rected forwardly and'the otherfrearwardly. In thear equally between the second and third arms.

to 31 made smaller than the spacings of the rows 20 to 25 so that the squint angle ,8 is positive for one set and negative for the other set. To obtain the necessary switching of the beams to produce the four beams as described above, this transverse feed waveguide may be fed from either end by means of a switch coupling either end of the guide alternatively to the transmitter and receiver of the Doppler navigation system. Preferably, however, to ensure equal division of the power from the transmitter between the two sets of rows 20 to 25 and 26 to 31, these two sets of rows are fed from separate transverse feed guides 32, 33 as shown in FIGURE 2. The transmitter and receiver of the Doppler navigation system, indicated diagrammatically at 34 can be connected alternately, by means of a switch 35, to one or otherof two power dividers 36, 37 which divide the transmitter output between the two transverse feed guides 32, 33. These power dividers serve also to combine the received signals for feeding through the switch 35 to the receiver. In this ar rangement the guides 32, 33 may be of different section so that the required squint angles can be obtained if desired, with similar spacings for the rows 29 to 25 and the rows 26 to 31. The switch 35 enables the phase relationship of the various rows to be reversed and thus, provided in each set the conductances of the couplings from the transverse feed guide to the various rows are symmetrical, switching of the feed from one end to the other of the feed guide will reverse the squint angle without altering the angular width of the beam or the depression angle. The various rows are terminated with dummy loads 38.

FIGURE 3 is an isometric view from the underside of one embodiment of the aerial array of FIGURE 2. Referring to FIGURE 3 there are illustrated parts of the waveguides 20 to 31. These are rectangular guides and ti will be seen that the waveguides 20 to 25, as illustrated on, guides 20 to 22, have radiating slots 40 in a narrow face of the guide, which slots slope alternately in opposite directions so that alternate slots would radiate in phase opposition if they were fed in phase. The waveguides 26 to 31, have radiating slots 41 which are parallel to one another and which radiate in phase if fed in phase. For clarity in the drawing only some of the slots 40, 41 are shown. The slots are formed in the narrow faces of the waveguide and face downwardly when the aircraft, in which the array is installed, is in a normal flying attitude. All the radiating slots thus lie in a horizontal plane. The waveguides may be mounted on a suitable mounting plate 42, for example a honeycomb structure made of aluminium, of which for clarity in the drawing only part is illustrated.

To feed the various waveguides 20 to 31 there is provided an input guide 45 which, by means of an E-plane right angle bend feeds into a rectangular guide 46. Lying behind the guide 46 in FIGURE 3 and extending parallel thereto is another rectangular guide 47. and these two guides have coupling slots from one to the other to form 3 db directional couplers as is more clearly illustrated in FIGURE 4. 50 and 51 each represent a 3 db directional coupler. The numbers 1, 2, 3 and 4 are marked against the various arms of the couplers to identify these arms; the notation used is such that any signal fed into the first arm is divided The first and fourth arms are de-coupled from one another as are the second and third arms. The input guide 45 is connected to the first arm of the 3 db directional coupler 49 so that the input signal is divided equally between the second and third arms of the coupler 49. In the outputs from the second and third arms of the coupler 49 is arranged a switch, indicated diagrammatically by a transverse dashed line 52, which can be operated either to put a short-circuit or an open-circuit across the two guides. Assuming the switch is in the open-circuit condition, all the power from the transmitter is divided between the second and third arms of the coupler 49 and these arms are connected to In FIGURE 4, the four rectangles 48, 49,

the first and fourth arms of the coupler 50 so that this power is all fed out through the third arm of the coupler 50. This arm is connected to the fourth arm of the coupler 51 so that the input signal thereto is divided equally between the second and third arms. These two arms are coupled by E-plane bends 53, 54 respectively to feed guides 55, 56 (FIGURE 3) which eXtend back across the ends of the rows. The feed guide 55 extends across the ends of the waveguides 26 to 31 to feed those guides through coupling slots and extends around the underside (the top in FIGURE 3 which is an underside View) of the waveguides 20 to 25. The feed guide 56 extends behind the ends of the waveguides 26 to 31 and then across the ends of the waveguides 20 to 25, being connected by coupling slots to feed the latter. If the switch 52 puts a short-circuit across the third and fourth arms of the coupler 49, the input power from the transmitter is all reflected back into the fourth arm, which arm is connected to the third arm of the coupler 48. The signals fed into the third arm of the coupler 43 are divided equally between the first and fourth arms which are connected by E-plane bends 57, 58 respectively to the second ends of the aforementioned feed guides 55, 56. It will thus be seen that, by changing the condition of the switch 52, the transverse feed guides 55, 56 may be fed from either end.

The switch 52 might be a mechanical switch e.g. a plunger or paddle in the waveguides or it might be an electrical switch e.g. a ferrite device controllable by an electrical signal to give open or short-circuits as required.

The guides 2tl25 and the guides 2631 are fed in antiphase, that is to say alternate guides are fed in phase opposition, to enable a small squint angle to be obtained and the spacing of the guides 2025 and of the guides 26- 31 and the sections of the feed guides 55, 56 are chosen, as previously described, so that the squint angles are of equal magnitude but opposite sign. of the couplings of the feed guide 55 to the guides 26 to 31 and of the couplings of the feed guide 56 to the guides 20 to 25 are made symmetrical so that, by changing the condition of the switch 52, the phase relationship of the feeds to the various guides in each set may be reversed to switch the beams whilst not altering the beamwidths or depression angles.

If the feed guides 55, 56 are fed from the coupler 51, then any wasted power passing down the feed guides and flowing out of the far end will pass into the first and fourth arms of the coupler 48 and thence be divided between the second and third arms of that coupler. A dtunmy load 59 is connected to the second arm of this coupler to absorb power fed into that arm and any power fed into the third arm is absorbed in a dummy load 61 connected to the second arm of coupler 50. Likewise, if the feed guides 55, 56 are fed from the coupler 48, any wasted power flowing out at the far end of the feed guides into the coupler 51 is half absorbed in a dummy load 61 connected to the first arm of coupler 51. Due to the switch 52 being in the short-circuit condition the other half is absorbed in the dummy load 60.

Considering the system in the receive condition, it will be seen that, when the switch 52 is in the open-circuit condition, any signals received and fed to the fourth arm of the coupler 51 will pass into the input guide 45 without loss and that, when the switch 52 is in the shortcircuit condition, signals received and fed to the third, arm of coupler 48 will pass to the input guide 45 without loss.

FIGURE 5 illustrates a modification of the arrangement of FIGURE 2, in which the waveguides forming one of the arrays of the radiating slots are interlaced with the waveguides forming the other array, that is-to say the waveguides forming the two arrays are arranged alternately in the same plane. Referring to FIGURE 5, one array comprises waveguides 61 to 66 having slots radiating in phase, whilst the other array comprises Waveguides 71 to 76 with slots radiating in anti-phase. In

The conductances FIGURE the rows forming the two arrays are shown as being fed from the separate transverse feed guides 80, 81 fed in parallelfrom one or other end from the Doppler system transmitter andfreceiver 82 by operation of a switch 83 which couples the transmitter and receiver to one or other of two, power dividers 84 85 for dividing the powerequally between the two trans-1 verse feed guides. The waveguides 71.to 76 are fed in anti-phase from the feed guide 81 and the waveguides 61 to 66 are fed in anti-phase from thefeed, guide 8t). The system thus produces two beams simultaneously and can be switched to produce the second pair of beams exactly as the arrangement of FIGURE 2.

FIGURE 6 is'an isometric view from the underside of one embodiment of theaerial system of FIGURE 5, and it will be seen in FIGURE 6 that the waveguides system which is a modification of that of FIGURE 2 The same reference numerals are used as in FIGURE2 i to indic'ate'co'rresponding' features. In FIGURE 9, there is only one transverse feed" guide 130' feeding all the forming the radiating array of slots comprise rectangular waveguides with the slots in their narrow faces. In T pling guides from the transverse feed guide 81, and simi- URES 5 to 7 and of FIGURE 8 areinstalled inan air larly the waveguides 61 to 66 arefed from-the transverse feed guide 80. The feeds to the guides 71 to 76 arein anti-phase, as are the feeds to the guides 61 to 66 and the coupling conductances for each set are made symmetrical so that the squint angles can be reversed Withoutchanging the beam widths or depression angles by revising the connections to the ends of the feed guides 80, 81. The power dividers 84, 85 and switch 83 are arranged in a unit 86 on the ,top ofthe aerial system as shown in FIGURE 7 having an input guide 87 for the connection to the transmitter and receiver of the navigation system. The unit 74 maycomprise four 3 db directional couplers and a switch similar to that describedwith reference to FIGURE 4. t

In the construction of FIGURES 6 and 7, the spacing of the waveguides 71 to 76 must be the same as that of waveguides 61 to 66 and hence the necessary phase relationship of the feeds to produce equal and opposite squint'angles is obtained by. using different sections for the transverse feed guides 81, 82.

The waveguides 71 to 76 and 61 to 66 are mounted on a mounting plate 76 which may conveniently be an aluminum honeycomb structure.

Instead of reversing the squint angles by switching the feeds to opposite ends of ,the transverse feed guides as in the arrangement of FIGURES. 2. to 4 and,5 to 7, it. depression angles by switching V the feeds to opposite ends of the rows of radiating slots.

is possible to reverse the One such arrangement is illustrated in FIGURE 8 in which there are shown diagrammatically rows 101 to 106formed of waveguides with slots arrangedto radiate in phase and rows 111 to 116 slots arranged to radiate in anti-phase. All the rows 101 to 106 and111 to 116 can be fed in anti-phase from one end by means of a transverse feed guide. 12001" from the other end by means of a transverse feed guide 121,

the two transverse feed guides being alternatively con-- formed of waveguides with either endof the feed guide, t

natively thateach of the feed guides 120, 121 might be replaced by twoseparate feediguides, one feeding the rows 101 to 106 and the other feeding the rows 111;to 116, these two guides being fed in parallel-from the the depression angleof the beam fromeach V 7 set of rows without altering the'squin't angles;

'FIGURE 9 illustrates another 'construction of, aerial i rows 20-25 and 26 to 3 1 of'radiating slots; Reversal of the squint angle *is effected 'by 'the switch 35 which connects thetransmitter and receiver alternatively to The aerial systems of FIGURES 2 014: in of as craft with the, rows, of radiating slots extending 'inthe fore-and-aft direction of the aircraft "and'in a horizon tal plane when the aircraftis in a normal'flying attitude.- 1 The aerial system may be stabilized if necessaryeeither in the, pitch plane'alone or completely stabilized." It

will be seen/that the arrangements described provide more it will be particularly noted that the squint angles,

the'slots in each row of one set being; phased radiating slotsv to produce cooperatively a first directional beam and the, slots in each row ofthe otherset being anti-phase V. radiating slots to produce cooperatively a second .di-;

, rectional beam ina direction, compared'to said first beam, r

' on the opposite side of 'a plane normal to the directiorr of said rows, a first transverse feed guide feeding one set.

of rows, and a second'transverse'feed guide feeding the 7 other set of rows, thegtwo transverseffeed guides' having different sectionsto2give different guide wavelengths and the spacing of the rows in each of the'two sets being" equal, the transverse feedguide 'sections'being such that the resultant different phaserelationship of the feeds to tion of the-rows.

are provided a signal source and means coupling said signal source to said first and second transverse feed guides to energise said feed guides in parallel;

nected to a transmitter and receiver 122 by means of a 7 switch 123. In this arrangement, to'ensure' that similar radiation patterns (apart from the change m direction of the beams) are obtained in thetwoswitch conditions,

the conductances of the radiating slots are made symmet.-; rical about the centre points of the rows.' If j the feed guides 120, 121 are of uniform cross-section, the spac- 3. An aerial system as claimed in claim 1 whereinithe 7 rows of one set are 'ar'rangedalternatelywith the rows of the other set. .7 a

4. An aerial system for usein microwave Doppler, alrborne navigational equipment comp'risingian array formed of twosets ofparallel rows of radiating slots;

each'set comprising anumberof rows .sideby. side with the'slots in each rowof one set being phased radiating ing of the rows 111 to 116 may be made different'from the spacing of rows 191 to 106 to give the required (lif ferent squint angles; 'It will be readily apparent how- I ever that the feed guides might have portions of dilferent section for feeding the two sets of rows or alterslots and the slots in each row' of the other set being ,f anti-phaseradiating slots, a first transverse feed" guidef feeding one set of rows, asecond transversefeed'guide feeding theoth'er set ,of'rows, the two transversefeed I 'guides'having different sections to givedifferent guide wavelengths andthe' spacing of the rows in eachof the two sets being equahthe transverse feed 'guidesections. being such that the resultant different phase relationship of] i the feeds tothe rows of the two sets produce equal'angle s:

2. Anaerial system as claimed in claim l ivherein there i of deflection of the two beams, radiated, respectively by the two sets of rows, in opposite directions transversely to the direction of the rows, a signal source, and switchable connecting means for coupling said signal source alternatively to one end of each of said first and second transverse feed guides or to the other ends of said first and second transverse feed guides.

5. An aerial system for'use in microwave Doppler airborne navigational equipment comprising an array formed, of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of 'one set being phased radiating slots and the slots in each row of the other set being anti-phase radiating slots, a signal source, transverse feed guide means feeding all the rows through coupling slots, and switch means for coupling said signal source to energise said feed guide means alternatively from either end, the coupling slots'being positioned in said transverse guide means so that the phase relationship of the feeds to the rows in one set is different from the phase relationship of the feeds to the rows in the other set so as to produce deflections of the two beams, radiated respec tively by the two sets of rows, in opposite directions transversely to the direction of the rows, and the coupling slots having symmetrical slot conductances so that radiation patterns of similar form but in different directions are obtained in the alternative settings of said switch means.

6. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of one set being phased radiating slots and the slots in each row of the other set being anti-phase radiating slots, the rows of one set being arranged in a group to one side of the rows of the other set, and a transverse feed guide consisting of a single length of waveguide coupled to all the rows of the two sets, the spacings of the feed points of the rows in one set differing from the spacings of the feed points of the rows in the other set to give different phase relationships of the feeds, the spacings giving phase relationships such that there are produced equal angles of deflection of the two beams, radiated respectively by the two sets of rows, in opposite directions transversely to the directions of the two rows.

7. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of one set being phased radiating slots to produce co-operatively a first directional beam and the slots in each row of the other set being antiphase radiating slots to produce co-operatively a second directional beam in a direction, compared to said first beam, on the opposite side of a plane normal to the direction of said rows, a signal source, a single transverse feed guide coupled to all the rows in both sets, and switch means for connecting said signal source alternatively to either end of said feed guide.

8. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of one set being phased radiating slots to produce co-operatively a first directional beam and the slots in each row of the other set being antiphase radiating slots to produce co-operatively a second directional beam in a direction, compared to said first beam, on the opposite side of a plane normal to the direction of said rows, a signal source, a single transverse feed guide coupled to all the rows in both sets, with the phase relationship of the feeds to the rows of one set being different from the phase relationship of the feeds to the rows in the other set with the two phase relation- 10 ships arranged to produce equal angles of deflection of the two beams radiated respectively by the two sets of rows, in opposite directions transversely to the directions of the rows, and switch means for connecting said signal source alternatively to either end of said feed guide.

9. An aerial system as claimed in claim 8 wherein each row is fed from a separate coupling slot in said transverse feed guide, the slot conductances for each set of rows being symmetrical so that similar radiation patterns are obtained with either end of said transverse feed guide being fed.

10. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of one set being phased radiating slots and the slots in each row of the other set being anti-phase radiating slots, a first. transverse feed guide coupled to all the rows of both sets at one end of each row, a second transverse feed guide coupled to all the rows of both sets at the other end of each roW, a signal source and switch means for connecting said signal source alternatively to either said first feed guide or said second feed guide.

11. An aerial system as claimed in claim 10 wherein the radiating slots in each of the rows have symmetrical conductances so that similar radiation patterns are obtained with either end of the rows of radiating slots being fed with the directions of the patterns reversed about a plane through the rows at right angles to the direction thereof.

12. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of parallel rows of radiating slots, each set comprising a number of rows side by side with the slots in each row of one set being phased radiating slots and the slots in each row of the other set being anti-phase radiating slots, first transverse feed guide means arranged to feed the rows of both sets from one end of each row, second transverse feed guide means arranged to feed the rows of both sets from the other end of each row, a signal source, and switch means for connecting said signal source alternatively to either said first or said second feed guide means.

13. An aerial system as claimed in claim 12 wherein the two feed guide means feed the respective rows in similar phase relationships, the phase relationship of the feed to the rows of one set being different from the phase relationship of the feeds to the rows of the other set with the two phase relationships producing equal angles of deflection of the two beams, radiated respectively by the two sets of rows, in opposite directions transversely to the direction of the rows.

14. An aerial system as claimed in claim 13 wherein the radiating slots in each of the rows have symmetrical conductances so that similar radiation patterns are obtained with either end of the rows of radiating slots being fed, the directions of the patterns being reversed about a plane through the rows at right angles to the direction thereof.

15. An aerial system for use in microwave Doppler airborne navigational equipment comprising an array formed of two sets of rows of radiating slots, each set comprising at least two rows side by side with the slots in each row of one set being phased radiating slots to produce cooperatively a first directional beam and the slots in each row of the other set being antiphase radiating slots to produce cooperatively a second directional beam in a direction, compared to said first beam, on the opposite side of a plane normal to the direction of said rows, a first transverse feed guide feeding one set of rows, and a second transverse feed guide feeding the other set of rows, the two transverse feed guides having different sections to give different guide wavelengths and the spacing of the rows in each of the' two sets being equal, the transverse feed guide sections being such that the resultant different phase relationship of the feeds to 'the rows of the two-sets produce equal angles, 'of deflection of the two vbeams, radiated respectively by the two sets of rows, in opposite directions transversely to the direction of the rows.

16, In Doppler airbornenavigational equipment, a transmitter, a first waveguide having a set of phased radiatingslots, a second waveguide having a set of antiphased radiating slots, a first feed system feeding one end of said first waveguide and one end of said second enga es 7 one end of said first waveguide and one end of said sec-. ond Waveguide, a second feed system coupled to theothe'r waveguide, a second feed system feeding the other end 1 ofsaid first waveguide and the other end of said second waveguide, and switch means arranged for connecting said transmitter alternatively to said first feed system or said second feed system.

'17. In Doppler airborne navigational equipment, a-

receiver, a first waveguide h'aving a set of phased receiving slots, 2. second waveguide having a set of antiphased receiving slots, a first feed system coupled to feed systems.

end ofv said first waveguide and the other endof' said second waveguide, and switch means arranged .for; con,-'

nectingsaid receiver alternatively to said first and second References Cited the file jof this patent 5 UNITED STATES PATENTS V V Washburne Apr. 25,1961 

7. AN AERIAL SYSTEM FOR USE IN MICROWAVE DOPPLER AIRBORNE NAVIGATIONAL EQUIPMENT COMPRISING AN ARRAY FORMED OF TWO SETS OF PARALLEL ROWS OF RADIATING SLOTS, EACH SET COMPRISING A NUMBER OF ROWS SIDE BY SIDE WITH THE SLOTS IN EACH ROW OF ONE SET BEING PHASED RADIATING SLOTS TO PRODUCE CO-OPERATIVELY A FIRST DIRECTIONAL BEAM AND THE SLOTS IN EACH ROW OF THE OTHER SET BEING ANTIPHASE RADIATING SLOTS TO PRODUCE CO-OPERATIVELY A SECOND DIRECTIONAL BEAM IN A DIRECTION, COMPARED TO SAID FIRST BEAM, ON THE OPPOSITE SIDE OF A PLANE NORMAL TO THE DIRECTION OF SAID ROWS, A SIGNAL SOURCE, A SINGLE TRANSVERSE FEED GUIDE COUPLED TO ALL THE ROWS IN BOTH SETS, AND SWITCH MEANS FOR CONNECTING SAID SIGNAL SOURCE ALTERNATIVELY TO EITHER END OF SAID FEED GUIDE. 